This application for an ADAMHA Research Scientist Award has two broad objectives: (1) to investigate perceptual and cognitive aspects of infants' reaching and grasping; and (2) to understand adults' localization of sound under varying acoustic conditions. The infant research will focus on the effects of vision in reaching because of the central role vision plays in specifying spatial location of object and hands. We will delineate and describe how infants use vision and proprioception to control reaching for objects by presenting visible and not visible objects. Infants between 2 and 13 months of age will be tested while reaching for objects in the light and for luminous and sounding (nonluminous) objects in the dark. Objects will differ in size, orientation, and location. The hand's approach and grasp of objects under various conditions should reveal whether infants prepare their hand appropriately to grasp an object when they can see both object and hand, only the object, or neither. Overt behavior will be videotaped and analyzed for interactions with the object. In addition a detailed analysis of hand movement during the reach by means of a motion analysis system will yield velocity, acceleration, and distance in 3-dimensional space for hand and object. Cognitive abilities can be inferred from certain aspects of motor activity, such as hand shaping and the approach trajectory for an unseen object in the dark. Our lab recently acquired a computerized motion analysis system which is necessary for this work, so a major challenge will be the extension of my technical skills in mastering this system. The adult research concerns the stimulus parameters that affect inhibition of echoes. Usually we do not hear echoes when there is a short time delay between the original sound and delayed sound (echo). During the previous RSA period we discovered that prior stimulation acts to increase echo threshold, whereas a rapid switch in spatial location between the original and delayed sound will decrease threshold. A series of studies will be conducted in an anechoic chamber where input to the ears can be controlled in free field. We will attempt to determine how adults use acoustic information contained in the sounds to suppress echoes. The research on adult auditory perception represents a new area for me, begun only 4 years ago. Plans for increasing both my technical expertise and background knowledge are integral for the success of this project.